gasoline tank for Mercedes TN 310 1992

I am looking for a left gasoline tank for my Mercedes TN 310 4x4 1992. It has an 80 liter tank on the right side (Austrian vehicle) but I need to increase my capacity. Now I know gasoline is not the first choice when it comes to overland travel. A second option would be to add a LPG tank. I prefer the first.
I thought it could be an English tank, but I am not able to find one on internet. I was told the English Gasoline tank is on the left side of the vehicle. under the car is the same space still void so it should fit. Can someone help me with an internet address or other option, likea custom made tank.
thanks,